If you can't find one that you're looking for than Southern Insulation in Fort Lauderdale can make you a soft sound shield for a reasonable price.
Great Southern Insulation made one for my first Bertram way back. Current Bert was missing the front panel and they made me just that one which I picked up from them in a warehouse, I think was in Plantation, where they had moved after Ft. Laud. location. I recall emailing them a sketch of the size and desired opening panels and even though owner was out of town when ready, his employee met me at the shop to pick up.
The 8kw Onan in my previous boat was a lot older with about 25,000 hrs and still running strong when I sold the boat. Current Northern Lights is 1996. No smoke, no issues and my home's back up 15kw, although only 325 hrs but bought back early 2000's only ever replaced a rusted exhaust pipe & several batteries & solar panels, and when I test now and then, still runs entire home including the 2 AC units.
I added substantial sound proofing to the walls and ceiling around the gens to leave them open for visibility access, killed a lot of sound without hiding problems.
Try getting parts for the OPs 15kw Westerbeke and report back. That's where the problem lies, same with the old 20kw Onans, which were great generators, you just can't get most parts for them anymore.
If I remember the ole Westerbroke sets used Mitsubishi engines. Whole different monster vs the Kubota usually in the ole 8 & 9 KW OhNos. These lil engines (not the OhNo hang on garbage) may never die. I have worked on many gen-sets including red-neck (Frankensteined) packages, including my personal "lil gen-set". I could type stories on all the gen-set brands but the historically hardest to get parts and support for was Westerbroke AND Mitsubishi spares. Their sound boxes at one time used rubber clamps to hold the panels up. One of my customers use adhisive velcro straps while his rubber clamps were on back order,, again.. Yet somehow, there is still a Westerbroke fan & customer base with smiles. ☺ Bless them.. Here in the swamps, just replacing something, that is running (for today), were not in a hurry to replace it. Even if it is a Westerbroke. Chances are any original sound box panel or parts you may find is not usable and past reef material candidate material. Probably the easiest, cheapest way to cover an old get-set is with the sound blanket. Or build your own panel that will screw or clip on over the existing hole. I wish the OP good luck in his search.
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